I spotted a T-shirt at school bearing this inscription, but I don't think it quite means what some people assume it means.

I take it that it's supposed to mean "end hate." But when you use a tag like </i>, you don't mean "end italics" in the sense "abandon italics forever." You mean "I've been using italics for a bit, I'm stopping for a while now, but I'll get back to using it later."

Substitute "hate" for "i," and you'll get my drift. I bet the guy has a <hate> T-shirt in his closet that he was wearing three days before; he's hated all the stuff between then and the </hate> shirt; and he'll be wearing the <hate> shirt next time he's got some hating to do. Plus he certainly wouldn't just wear the </hate> shirt without having worn <hate> before, and on the same page -- that would be syntactically non-compliant.